The present invention relates generally to lasers and in particular to controlling fiber coupling between a laser, a modulator, and an optical output.
Tremendous amounts of data can be transmitted quickly across a fiber optic or free space link using lasers. This is typically accomplished by modulating the lasers. In one technique, a single laser is turned on and an external modulator is used to modulate the light with an input data signal. Performance of this technique is usually good, since external modulators can be constructed with controlled and adjusted chirp.
However, coupling the light from the laser, to the modulator, and then to the output fiber, and making sure that this tight coupling is maintained through life of a transmitter is challenging and adds to the cost of such transmitters. Furthermore, some modulators are extremely sensitive to strain and as a result are sometimes packaged on a compliant material, making an integrated laser modulator package even more challenging. Because of the compliant packaging of the modulator, the position of the modulator is often not well controlled and can move around. Therefore, generally, the modulator and laser are generally connected together with an intermediate piece of optical fiber. The laser and the modulator are thus separately fiber coupled, and the two are spliced together. This extra fiber coupling, coupling light from a laser to a fiber optic cable via a modulator, is typically needed but is often a costly step in packaging various waveguide devices for telecommunication applications. In general, any fiber coupling is a costly and time consuming process, on account of the very small optical modes in single mode waveguide devices. Thus, very tight submicron tolerances are often required in the packaging. Typically, when the fiber coupling is maximized, the optical elements are permanently fixed in position. The process is often not very reproducible due to contraction in epoxies or thermal expansion of the components.
The present invention provides an adjustable optical coupling systems and methods for tunable lasers and modulators. In one aspect of the invention, a laser emitting a continuous optical signal and a modulator are provided. Also, an adjustable element steering the optical signal to a position on the modulator is provided. A controller manipulates the adjustable element to maintain the optical signal to a specific position on the modulator.
In another aspect of the invention, a laser is selected from an array of lasers, each laser emitting light at differing wavelengths. Also, an optical path from the laser to a modulator is established and the optical path is adjusted to maximize, balance or otherwise adjust output power from the modulator. Also, a reverse bias current on the modulator is monitored to determine the position of an optical element.
In another aspect of the invention, light from the modulator towards the laser array is prevented. Also, an optical path from the modulator to an optical output is established to maximize, balance and otherwise adjust power of the light from the modulator and a modulator from an array of modulators is selected. In one aspect of the invention, the modulator is selected based on the laser selected, a specific chirp value and/or reducing a bit error rate. In another aspect of the invention, voltage on the at least one modulator is adjusted.
In yet another embodiment, one or more lasers, one or more optical elements and one or more modulators are provided, such that light from a laser is directed into a modulator by one or more optical elements. Also, a controller is provided and is configured to adjust the one or more optical elements to adjust output power of the light directed into the at least one modulator. Also, the controller is configured to adjust the one or more optical elements based on a reverse bias current through the one or more modulators.
In another embodiment, emitting means for emitting light having different wavelengths and modulation means are provided. Also, optical means directs light having a particular wavelength from the emitting means into the modulation means. Furthermore, control means is coupled to the optical means and adjusts the optical means to maximize or balance or otherwise adjust output power of the light directed into the modulation means.
Many of the attendant features of this invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings.